A new polymer inclusion membrane-based system to separate and determine copper ions in saline waters

We present a new system to separate and determine copper concentration in saline samples. It is based on the use of a polymer inclusion membrane (PIM) to separate and preconcentrate the copper ions from the saline aqueous matrix to a receiving acidic solution. The influence of the composition and thickness of the PIM has been studied and optimised, by varying the concentration of the base polymer, extractant reagent, and plasticizer, as well as the total volume of solution used to prepare the membrane. The thinner PIM exhibited the best transport of metal ions, with the optimal thickness of 20.5 ± 1.8 μm and the composition being 30% (w/w) of cellulose triacetate (CTA), 60% (w/w) of di(2-ethylhexyl) phosphoric acid (DEHPA), and 10% (w/w) of tris(2-ethylhexyl) phosphate (TEHP). In addition, we studied the influence of the physico-chemical variables on copper transport across the membrane. Optimum results were obtained for a sample pH of 5 and a stripping phase containing 0.1 mol L^-1 HNO₃. The variation of copper concentration was monitored on-line by using a colorimetric reagent containing 6.67x10^-5 mol L^-1 of 4-(2-pyridylazo) resorcinol (PAR) in a flow injection analysis (FIA) system. A second-order mathematical relationship was obtained between the extraction time and the percentage of copper separation, enabling the application of the method to real seawater samples with different copper concentrations at the ppm and sub-ppm levels.